INSKEEP: This is a headline we haven't heard in a while. Car sales have been very strong, but sales of cars and trucks in the United States fell last month by four percent industrywide. It's the first monthly decline in auto sales in more than two years.

RENEE MONTAGNE, HOST:

NPR's Sonari Glinton reports the drop-off has as much to do with the calendar as the economy.

SONARI GLINTON, BYLINE: August was such a good month that it may have stolen some of September's glory. Kelley Blue Book's Alec Gutierrez.

ALEC GUTIERREZ: There are two fewer selling days this year versus September of 2012. And also Labor Day sales, which are typically some of the best sales throughout the entire year, were counted in the month of August rather than September.

GLINTON: I was going to list all the car companies that saw sales drop off, but that would take way too much time. I'll just go with the ones that did OK: Chrysler, Ford, Daimler - that's Mercedes. Subaru and BMW saw gains, along with some super-duper luxury car brands like Maserati and Jaguar. Almost everyone else - bit it.

JESSICA CALDWELL: We've seen, you know, debt ceilings. We've seen global economic crises. And the fact of the matter is people still need cars. They need to get to work. They need to get to school. And, you know, if interest rates are low and there is that need out there, car sales will continue to thrive.

GLINTON: Caldwell says as long as the economic fundamentals stay up, so will car sales.